UNHAIRING HIDES 



SULPHIDE OF SODIUM. 



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UNHAIRING HIDES 



SULPHIDE OF SODIUM. 



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JAM 8 188d\ 



CUTLER, HALL & BORCHERS, 



Colonial Chemical Works, ^ '^'•^^nTi 



Okfice : Mason Building . . . Kilby Street, 

Boston, Mass. 



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Copyright, 1883, 
By Cutler, Hall & Borchers. 



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UNHAIRING HIDES BY SULPHIDE OF SODIUM. 



The aim of this pamphlet is not to expatiate on the virtues 
of some new, untried, and merely experimental method of 
unhairing, whose chief merit consists in large claims and great 
pretensions, but it is to give a more extended notice to tanners 
here of the advantages to be derived from the use of an agent 
in unhairing hides, which is well known in the Old World, 
and which has afforded most satisfactory results to the com- 
paratively limited number of tanners in this country making 
use of it. 

It is unnecessary here to state the disadvantages of the old 
lime process of unhairing, the dangers which attend the sweat- 
ing process, or the causes of failure of many of the other 
methods, both secret and non-secret, which have been from 
time to time advanced as the best means of accomplishing the 
desired end. 

There is one process, however, that of Prof Lufkin, to 
which your attention is called, because it is quite fully described 
and favorably commented upon by Mr, Jackson S. Schultz in 
his useful work on leather manufacture on pp. 34 and 35. Mr. 
Schultz, after speaking of the great success attested by the 
superior quality of leather produced, which Mr. Charles Cooper, 
of Sparrowbush, N. Y., obtained by the employment of this 
process, goes on to say : — 

" His packs were made up of about fifty hides each, either 
cured, green, salted, or dried, Buenos Ayres or Rio Grande. 
The green hides weighed fifty and the dry twenty pounds 



each. For such a pack he would slake eighty pounds of stone 
lime, . . . except that the lime is not watered after the 
slaking process has been finished. This leaves the lime of 
the consistency of a thick paste. While in this state take a 
small portion and knead thoroughly with ten pounds each of 
soda-ash and pulverized sulphur. When these three products 
are well mixed, and while the lime is yet warm, turn the whole 
in together and mix thoroughly ; after doing this, take lime 
liquor from the vat and fill the cask, stirring all the while. 
When completed, pour into the vat and thoroughly plunge the 
whole. . . . As to the advantages of this process, the writer 
would say that the sulphur modifies the harshness of the lime 
and soda-ash, and renders them almost as controllable in the 
hide as soft soap ; for, while the hide may remdiin in the lime 
for an equal length of time as with the old process, there is 
not the same swelling, nor the same harshness, and a few 
minutes of wheeling in warm water will reduce the pelt to 
almost the consistency obtained in sweat stock. There is no 
question that it is a good method of Jinhairing for all kinds of 
hides or skins, and when a soft and smooth grain is desirable, it 
is a valuable improvement. Of course it is slightly more expen- 
sive than pure lime, and for this reason has not found general 
favor." 

The effective substance in the above-described process, so 
favorably noticed by Mr. Schultz, is nothing more nor less than 
sulphide of sodium ; but the mode of obtaining it is primitive, 
crude, and unprofitable in the extreme, subjecting the tanner to 
a waste of material, a loss of the proper chemical effect through 
imperfect and unscientific composition of the substances, and, 
in addition, to unnecessary expense. 

To illustrate by one example only, of the above mixture, at 
least four pounds of sulphur are lost by being oxydized, even 
if worked very carefully, while still more is rendered useless 
by not becoming dissolved at all. 

Mr. Cooper's experience has demonstrated what good results 



have been obtained from the use of a very unskilfully com- 
pounded preparation ; while the efficacy and value of sulphide 
of sodium as a depilatory, when made on scientific principles, 
is testified to by its widespread use among the tanners of 
England and the Continent. Those of our own tanners who 
use the imported product so fully appreciate its worth in the 
production of superior leather that they endeavor to keep the 
knowledge of its use a secret from their fellow-tradesmen. 

All unhairing processes aim to change only the external por- 
tion of the hide sufficiently to allow the removal of the hair, 
leaving the rest of the hide intact in its original state; and, of 
all the means employed up to the present time to attain this 
end, sulphide of sodium comes the nearest to perfection. 

Sulphide of sodium is a disinfectant, and so arrests and not 
assists decomposition ; and, instead of dissolving the gelatine 
and fine fibres, as lime does, in a hide, thereby destroying 
valuable leather-forming substances, sulphide of sodium filter- 
ing through the hide affects only the hair and leaves the fibres 
intact and the cells unbroken, free from the deposit of any 
insoluble products, as carbonate of lime, etc., which cause the 
leather when tanned to crack. 

Another effect of the sulphide of sodium in the unhairing 
process is to plump the hides, if required ; but it does so with- 
out incurring the danger of pricking, which so frequently 
happens in the sweating process. 

I. Unhairing Hides for Sole Leather. 

A favorable circumstance, which adds much to the success 
of sulphide of sodium, is that the method of tanning following 
the unhairing is quite the same as if the sweating process had 
been employed. 

To unhair hides by the use of sulphide of sodium, the fol- 
lowing directions are to be observed: — 

The hides to be treated should first be soaked and washed, 



in order to render them as soft and clean as possible. *rhen 
dissolve one part of sulphide of sodium in two parts of hot 
water. The solution thus formed is too liquid, and, to avoid a 
wasting of material when the hairs are brushed over with it, 
it must be inspissated by slaked lime, whiting, or clay. Herr 
Eitner, managing president of the Institute for Leather Indus- 
try in Vienna, recommends slaking three parts of quicklime 
to one part of sulphide of sodium, and using the lime paste 
with the solution above described. We should recommend, 
however, the substitution of whiting or chalk for lime, as the 
latter favors an oxydation of the sulphide, which tends to 
destroy its effectiveness. A green hide requires one half to 
one pound of sulphide of sodium, according to the size and 
thickness of the hair; a dry hide requires one or two ounces 
more. The mixture is brushed over the grain side of the hide 
and worked down upon the skin, especial attention being paid 
to those spots where the hair is the thickest. Great care should 
be taken not to apply chalk containing such impurities as 
small stones or sand, because where they touch the hide the 
hair will not leave it. After the application of the mixture 
the hides are folded together and piled up in a moderately 
warm room, covered with fresh hides, or some moist stuff, to 
prevent their drying. In this process hides become plumped 
but little, and resemble very closely green or sweated hides. 

To facilitate the removal of the hair it is recommended 
that the hides be now placed in water for a short time, which 
has the effect of plumping them, and enables the hair to be 
cleaned off with ease. 

From this point the work of tanning proceeds in the same 
manner as if the hides had passed through the sweating 
process. It is necessary to state, however, that the above- 
described treatment is to be followed only when the tanner 
wishes to apply the sulphide of sodium on the grain side of 
the hide. Where circumstances require its application on the 
flesh side, as, for example, when it is desired to preserve the 



hair for other purposes, the hides should be afterwards folded 
together with the hair outside, piled up in a tank, covered with 
water, and allowed to remain twelve hours. On removal they 
will be found to present quite a different appearance from 
hides treated in the first manner, for the sulphide of sodium 
had to impregnate the pores of the hide before getting to the 
roots of the hair, the consequence of which is to plump the 
hide, thereby doing away with the necessity for those strong 
acid handlers which the others required, neutral ones fulfilling 
all purposes perfectly well. 

Hides thus treated take up more tannin than limed or 
sweated hides, and turn out much heavier and better leather, 
because the conditions under which they are prepared are very 
favorable to the absorption of the tan liquor. Sulphide of 
sodium not only produces no injurious effects upon the leather- 
forming substances in the hide, but assists the most perfect 
utilization of them yet obtained, there being no undue expan- 
sion of the fibre, no decomposition, and no destruction of the 
gelatine cells, — facts which alone recommend its use to every 
tanner desirous of producing leather of superior quality and 
weight. The average gain in weight over the old processes, 
according to the report of a reliable Austrian tanner, is 10.4 
per cent. 

II. UxHAiRiNG Hides for Inner Solings. 

The liming process is still extensively employed, and, as hides 
unhaired by the sulphide of sodium process, above described, 
while resembling greatly hides which have passed the sweating 
process, are quite different from those which have been limed, 
the treatment of them following the unhairing should be some- 
what changed, particularly during the first steps of the tan- 
ning process. Limed hides require weak, non-acid handlers, 
because the lime, by corroding, dissolves the gelatine, and also 
the most tender skin fibres, starts the plumping at the unhair- 
ing process, but at the expense of leather-forming substances. 



8 

Hides unhairedby an application of sulphide of sodium (Jh the 
grain side remain much in their natural state, — they require 
more acid to plump them, but there is more material left to be 
tanned ; they take up more of the tanning substances, and in 
consequence will furnish a greater gain in weight. If the 
sodium is applied on the flesh side, the hides will require less 
acid but stronger liquors than limed hides. These remarks do 
not apply to light hides coming from warm latitudes, which 
tanners here commonly treat by the sweating process, as the 
same directions for the application of sulphide of sodium are 
to be followed which are given under the first heading, — 
" Unhairing Hides for Sole Leather." 

In leather to be used for uppers or belting, where a certain 
quality of toughness combined with flexibility is the end 
desired, the liming process has been mainly employed, as 
this treatment is deemed the best for obtaining the proper 
separation and elongation of the fibres. This separation, 
which consists in dissolving the gelatine that binds the fibres 
together, is not only accomplished by the lime, but the latter 
works a dissolution of the most tender fibres, which, when the 
gelatine is removed, are carried along with it. By this means 
valuable leather-forming substances are destroyed, the capa- 
bilities for the absorption of tannin greatly decreased, and 
deposits of the insoluble portions of the lime (carbonate of 
lime) remaining in the hide tend to make the leather coarse 
and liable to crack. 

All these deleterious effects however are avoided, as above 
shown, by the use of sulphide of sodium. Hides to be 
tanned for belting must be washed after the hairs have become 
loosened, then unhaired and laid in water for two or three 
days, when they are scraped off" again. This done they are 
placed in water again, but only for a very short time, and then 
they are ready for the handlers. The handlers must be only 
slightly acid, but the tan liquor can gradually be used stronger 
than is common for this purpose. The number of baths 



should not be less than eight and may be as many as 
twelve. 

To prevent liquors from becoming sour, an addition of 
from one fourth to one pound of soda-ash, according to the 
size of the vats, or twice the amount of common salt, is recom- 
mended. 

III. Unhairing Hides for Upper Leather. 

After the hides have been washed, soaked, stretched, and, 
if necessary, fulled, the flesh side is brushed over with the 
sulphide of sodium mixture, the quantity being determined 
by the size and quality of the hides, and the hides are then 
folded, piled in a tank, and covered with water, as previously 
described. On removal from the tanks they are washed, un- 
haired, and fleshed. These hides are not plumped like those 
coming from the lime pits, neither are they in the proper state 
to be put into the handlers, but they first have to pass the 
operation of being bated. The principal aim here is to obtain 
suitable softness. After the bating they are trimmed, and 
then placed in the handlers and lightly colored. This method 
of treatment produces most excellent results, and is strongly 
recommended to tanners who use largely extracts, decoctions, 
or solutions (e. g., gambler, valonia, etc.). 

For tanners who use the bark itself it would be necessary 
to proceed as follows : Following the unhairing, which is 
accomplished by the same method as heretofore described, the 
hides must pass a plumping process. The wash water left 
from unhairing contains considerable quantities of sulphide 
of sodium, which, while of sufficient strength to plump calf- 
skins, is not strong enough for beef or other harder hides : 
these require the addition of about one quarter of a pound of 
sulphide of sodium per hide. One part of sulphide of sodium 
is dissolved in two parts of hot water and then added to the 
wash water, and the unhaired hides are hung in a vat contain- 
ing this liquid and allowed to remain three days, or longer, 



lO 

according to the degree of plumping which is required. The 
further operations, leaving out the trimming, are essentially 
the same as if the plumping had been done by the lime pro- 
cess. 

IV. System of applying Sulphide of Sodium as prac- 
tised IN England and Germany. 

We append herewith an account, necessarily much abbrevi- 
ated, of the simple and efficient system for unhairing in vogue 
among the tanners of the Old World, with the hope that its 
merits may recommend it to tanners here. A number of vats or 
large casks, determined by the requirements of the tannery, 
are placed side by side and connected with each other, by 
means of pipe at the top and bottom ; /. e., that is, connecting 
the bottom of the first vat vi^ith the top of the second, the 
bottom of the second with the top of the third, and so on. 
The hides are hung or laid in these tanks, and a solution of 
sulphide of sodium, made in the proportion of about six or 
eight pounds to ten or twelve gallons of water, is then run 
into the first vat at the top and, when attaining the proper level, 
is carried by its own force out at the bottom and discharged 
into the top of the next tank. The contents of the first tank 
receive the full strength of the solution, and consequently are 
the first to become "ripe." The fiov*^ of solution is then 
stopped, the valve in the connecting pipe closed ; what liquor 
remains is drawn out and emptied into the second tank. Tlie 
hides are then removed, and the tank is repacked with fresh 
ones. The first tank now takes the position of being last, in 
respect to being filled, and as, meanwhile, the contents of the 
second tank have become ripe, the process just described is 
repeated. 

The writer has seen sets of from six to fifteen tanks 
arranged in this manner, from which one or two were always 
disconnected, for the purpose of being repacked and refilled 



II 



while the h'quor was running through the rest, advancing their 
contents through the different stages to completion. Of course 
the size and number of the tanks or casks and the quantity 
and velocity of the solution to be run through them can only be 
determined by the circumstances which attend the require- 
ments of each tannery. The number of hides necessary to be 
unhaired per diem, the size, thickness, and kind, whether dry, 
salted, or green, and for what purpose the leather is to be 
used, are all points upon which the proper answering of 
this depends. 

As regards plumping, the degree requisite for the differ- 
ent qualities of leather can always be obtained by a proper 
regulation of the time during which the hides are to remain 
immersed. The explanation of this process can only be 
given here in a much too curtailed form ; but to any par- 
ties interested in this matter, we shall be happy to give 
more detailed information on application, and will furnish 
drawings for the proper construction of the tanks gratui- 
tously. 



In closing, we would summarize the advantages to be 
derived by the use of sulphide of sodium as follows: — 

Hides are unhaired in a shorter time and with greater 
perfection than by either the liming or the sweating pro- 
cess, without the dangers incident to both. The hides 
remain in the state most favorable for the absorption of 
tannin, and there is no loss of leather-forming substances by 
decomposition or dissolution. Plumping is accomplished 
with none of those injurious effects attendant on the other 
processes, and in sole leather, where weight is essential, it 
is gained at no sacrifice of material ; moreover, the neces- 
sity for the use of strong vitriol in the handlers beins; 
removed, the color of the grain is unaffected, and the 



12 

• 

leather can be butfed with the same good results as non- 
acid leather. 

One striking example of the advantages of the use of 
sulphide of sodium is the fact that tanning can continue 
through the warm weather of the summer months without 
interruption or extra expense, there being none of the dan- 
gers of too rapid decomposition and pricking, which is the 
case with the sweating process. In tanneries where water 
of a sufficiently low degree of temperature to arrest decom- 
position is not at hand in summer, and additional outlay for 
ice is required, the value of a process whereby the necessity 
for cooling hides is obviated is apparent. 

We shall cheerfully answer all inquiries made with regard 
to this product, furnish explicit directions for its use adapted 
to all kinds of leather, and forward samples by express to any 
address. 

To tanners whose attention is called to this process for the 
first time, we would say, the working sample offered by us 
will give you ample opportunity to test both the value of the 
product and the truth of what is claimed for it. The experi- 
ment costs nothing, for no apparatus is necessary ; and the 
trial can be made on one hide. 

Respectfully, 

CUTLER, HALL & BORCHERS, 
Ma7iiifacttirers of Sulphide of Sodium. 



LIBRARY OF CONGRESS 

016 055 548 8 



